Well I figured it out now.
Thanks Twiebie for your hint :)
The problem was. I used Globally BBCode Parsing ( Forums,Comments) and HTML Parsing just for Pages.
For adding normal news articles it choose html parsing automatically. But i18n uses the standard parsing method (in my case BBcode)
This opens a new question: When I want to use BBCode Parsing for Forums + Comments. How do I have to set up my system?
There should be a switch (choosing parsing method) in translation mode (like when you write normal news articles).
Thanks a lot four your help!
Added 6 minutes later:
For everyone wondering how it looks like when parsing method is set to bbcode with i18n
Adding normal article: